This invention relates to a process for the recovery of precious metals such as gold and silver from ores containing such metals by leaching and amalgamation techniques.
Typically the recovery process consists of crushing and grinding the ore, leaching it in an alkaline cyanide solution (cyanidation), then precipitating the gold from the solution, usually by addition of zinc dust.
Where there is much free gold occurring in the ore it is usually economically advisable to use a preliminary recovery step of amalgamation, corduroy tables, or flotation. Often 40-80% of the free gold can be recovered by the preliminary step at a cost lower than that of precipitation from a cyanide solution. A further benefit is the reduction of the process time required in the cyanide solution.
The Mining Engineers' Handbook, 3rd edition, 6th printing, p. 33-11, states that grinding in a cyanide solution is customary, unless the ore (a) requires preliminary washing, or (b) undergoes preliminary amalgamation or other treatment. It further indicates that in a cyanide solution recovery by amalgamation is reduced. This would indicate that simultaneous leaching and amalgamation would not normally be considered as an efficient and productive approach.
U.S. Pat. No. 4,384,889, Wiewiorowski et al., discloses a method wherein simultaneous leaching and cementation takes place. The concept of simultaneous leaching and amalgamation is not disclosed.
Other U.S. patents showing refining processes include U.S. Pat. Nos. 4,372,830; 4,427,571; 4,431,614; and 4,483,076.
It is an object of the invention to provide a novel and efficient method of extraction of precious metals.
It is another object of the invention to provide a method which will have particular application to extraction of gold and silver.